The present invention relates to the field of photography and, more specifically, to an adapter for operatively coupling an automatic camera to an optical instrument (such as a microscope, telescope, etc.) in position to photograph an image provided by the instrument.
In a preferred embodiment, the adapter is particularly designed for use with the SX-70 Land camera marketed by Polaroid Corporation, Cambridge, Massachusetts.
The SX-70 is a highly-automated, battery operated, single lens reflex, self-developing camera which upon actuation automatically proceeds through a preprogrammed cycle of operation. The cycle includes a preexposure phase during which the shutter closes and a rather large plate-like reflex member pivots from a viewing position to an exposure position; a film exposure phase wherein the shutter is automatically controlled by a light sensing circuit including a photocell mounted on the front of the camera next to the objective lens for measuring scene light; and a postexposure phase during which the exposed film unit is advanced between a pair of rollers for processing and ejection from the camera, the reflex member is returned to the viewing position, and the shutter is reopened.
Adapters for operatively coupling an SX-70 camera to the eyepiece tube of an optical instrument are known in the prior art. For example, see U.S. Pat. Nos. 3,999,195 and 4,176,931; and commonly-assigned U.S. Pat. Nos. 3,898,678; 3,900,858 and 4,021,825.
The last-mentioned patent recognizes that when the relatively heavy SX-70 camera is mounted on a slender microscope eyepiece tube and the reflex member is rapidly pivoted and then abruptly stopped at the exposure position, vibrations, persisting up to approximately two seconds, may be induced in the system and cause image blur during the film exposure phase.
The adapter disclosed in U.S. Pat. No. 4,021,825 solves this problem by providing an auxiliary capping blade shutter that blocks the camera objective lens prior to the start of the cycle. After cycle initiation and a period allowing the vibrations to subside, the auxiliary shutter is moved to an unblocking position to initiate the film exposure phase. The exposure is controlled by diverting a portion of the image forming light emanating from the microscope eyepiece to the camera mounted photocell with an elongated prism.
In effect, the auxiliary shutter allows the user to override the preprogrammed cycle by inserting a delay between the preexposure and exposure phases.
The adapter also is designed to operate in a manual mode for long, low light level exposures that exceed the camera's automatic cycle limit of approximately 20 seconds. In this mode, the cycle is initiated and then, after the shutter is opened for exposure, a film loading door latch is pivoted causing the battery in the camera to be disconnected from the camera control circuits thereby suspending the automatically controlled exposure phase. Exposure is manually terminated by moving the latch to reconnect the battery and then closing a switch to energize a lamp in front of the camera photocell which causes the shutter to close.
While the above-noted adapter performs well, it does have a limitation. Those skilled in the art of photographing optical instrument provided images will recognize that the light intensity level of these images vary considerably. Factors contributing to such variability include the light transmission or reflection properties of the specimen under observation, the amount of heat the specimen may be subjected to by the instrument's illumination system; the degree of magnification utilized; etc. Because the light intensity level is difficult to judge visually and the adapter does not include any means for measuring light intensity prior to film exposure, it is likely that the user will attempt sme exposures when the image forming light intensity level does not fall within a predetermined range of exposure values compatible with the camera's automatic exposure control system and the resulting print will be either overexposed or underexposed. This wastes film and places the burden on the operator to analyze the poorly exposed print and then estimate how much the illumination must be changed for correction.
Commonly-assigned copending applications U.S. Ser. Nos. 063,043 and 063,254 disclose an adapter for operatively coupling an automatic self-developing camera to an endoscope. The adapter includes a light sensing circuit, operable before camera actuation, for measuring the light output level of the endoscope and storing this information for later use in controlling exposure. Exposure is terminated by energizing a lamp in front of the camera photocell at a time following exposure initiation that is proportional to the stored information. The initial measurement is provided by pivoting a mirror or prism into the light output path ahead of the camera objective lens and diverting a portion of this light to a photocell mounted on the adapter. However, the adapter does not include means for inhibiting exposure if the measured level does not fall within a range that is compatible with the camera and film speed exposure parameters. Again, film may be wasted while the illumination system is experimentally adjusted.
U.S. Pat. No. 3,987,463 discloses a complex special purpose camera assembly and remote control unit designed for use with a microscope. The camera assembly includes a photocell for measuring the light output of the microscope before exposure initiation. If the measured light level is below a predetermined range, an indicator lamp on the control unit is energized to warn the operator. However, such a complex camera and control unit is inherently expensive and does not provide the option for using a relatively low-cost commercially available camera, such as the SX-70, for making properly exposed self-developing prints.
Cameras that include self-contained system for monitoring scene light before exposure initiation and inhibiting initiation of an automatically controlled exposure cycle if the scene light level is too high or too low and also providing a warning indication to the user in the viewfinder are also known in the prior art. For representative examples of such cameras or self-contained systems for use therein, reference may be had to U.S. Pat. No. 3,921,183 and commonly-assigned U.S. Pat. Nos. 4,007,469 and 4,174,893.
It is a principle object of the present invention to provide an adapter that is designed for use with a commercially available camera, such as the SX-70 Land camera, which does not include such a self-contained system and adds the preexposure light measurement and selective camera actuation inhibit function when the adapter embodying the present invention and such a camera are used in combination.
It is another object to provide such adapter which operates in an automatic mode that includes inserting a delay in the camera's preprogrammed cycle to allow vibrations induced by movement of the reflex member to subside before the film exposure phase is initiated.
Another object is to provide such an adapter that is easy to use and economically constructed.
Yet another object is to provide an adapter that is suitable for operatively coupling such a camera to a large variety of optical instruments and has a light measuring system that is accurate over the wide range of image intensity levels generally encountered in photographing images provided by these instruments.
Still another object is to provide such an adapter that is also operable in a manual mode for time exposures in excess of approximately 13 seconds and includes a simply constructed and easy to use manual mode actuating assembly.
Another object is to provide such an adapter that includes visible indicators for indicating when the measured light output level of the instrument is above or below a predetermined range of exposure values.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.